Preparation and characterization of spin crossover thin solid films
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Preparation and characterization of spin crossover thin solid films Tim Hochdörffer 1 & Juliusz A. Wolny 1 & Lena Scherthan 1 & Hendrik Auerbach 1 & Sadashivaiah Sakshath 1 & Andreas Omlor 1 & Sandra Wolff 2 & Hans-Christian Wille 3 & Ilya Sergeev 3 & Volker Schünemann 1
# Springer Nature Switzerland AG 2019
Abstract
Iron(II) spin crossover complexes display a reversible transition from low-spin (LS) state to high-spin (HS) state by e.g. variation of temperature, pressure or by irradiation with light. Therefore, these systems are promising candidates for information storage materials. In view of practical device applications thin films of these materials are needed. The SCO-compound [Fe(Htrz)2(trz)] (BF4) (1) switches between the LS and the HS state with a 50 K wide thermal hysteresis loop above room temperature. We have prepared thin films of 1 on a SiO2 substrate by spin coating. The spin states of the films have been characterized by Mössbauer spectroscopy in reflection mode using a MIMOS II spectrometer. A low quadrupole splitting (LS state) at 300 K and a high quadrupole splitting (HS state) at 400 K were found for the film, as well as for bulk powder of 1. This confirms that a spin crossover occurs above room temperature. Furthermore, synchrotron based nuclear resonance scattering measurements from 80 K to 400 K indicate that the hyperfine parameters are similar to those of the bulk powder of 1. DFT calculations reproduce the experimentally determined Fe-vibrational density of states of the bulk and of the thin film sample of 1. These results indicate that a higher fraction of HS Fe atoms is present in the film of 1. Therefore, we conclude different SCO properties of the thin film and the bulk material of 1. Keywords Spin crossover . Thin films . Mössbauer spectroscopy . Nuclear inelastic scattering
This article is part of the Topical Collection on Proceedings of the International Conference of the Application of the Mössbauer Effect (ICAME 2019) held in Dalian, China, 1-6 September 2019 Edited by Tao Zhang, Junhu Wang and Xiaodong Wang Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10751-0191671-y) contains supplementary material, which is available to authorized users.
* Tim Hochdörffer [email protected] Extended author information available on the last page of the article
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1 Introduction Some transition metal compounds, particularly those carrying 3d4-3d7 metal ions in an octahedral surrounding, display a transition between a low-spin state (LS) and a high-spin state (HS) upon external stimuli like temperature, pressure and illumination by light. This phenomenon is called spin crossover (SCO) and was first discovered in 1931 by L. Cambi [1]. SCO materials remain the subject of extensive studies due to (i) a dependence of the spin transition on small variations in ligand and crystal packing [2] and (ii) potential technological applications [3] like molecular switches, memory elements [4], te
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